Reductant Sensor System

ABSTRACT

An exhaust treatment fluid system includes a tank housing for storing an exhaust treatment fluid. A suction tube includes a first end positioned within the housing and a second end in communication with a suction port of the housing. An elongated laminar flow device is secured to a discharge port of the housing such that exhaust treatment fluid flows along surfaces thereof as the exhaust treatment fluid is returned to the tank housing. The laminar flow device includes a non-circular cross-section.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/820,216, filed on May 7, 2013. The entire disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to an exhaust after-treatment systemincluding a reductant sensor system.

BACKGROUND

This section provides background information related to the presentdisclosure which is not necessarily prior art.

Exhaust after-treatment systems may dose an exhaust treatment fluid intothe exhaust stream to assist in chemical reactions that remove NOx fromthe exhaust stream. The exhaust treatment fluid may be stored in astorage tank that communicates with a dosing module, which doses theexhaust treatment fluid into the exhaust stream. The storage tank mayinclude various sensors for determining a temperature of the fluidlevel, a fluid level in the tank, and a concentration of the fluid inthe tank. When the exhaust treatment fluid is a urea solution, thesolution may freeze in cold temperatures. To prevent freezing of theurea solution in the dosing module, the dosing module may be purged andthe unused urea solution may be returned to the tank. After beingpurged, the system generally must be primed before dosing of the ureasolution can resume. During the priming process, the urea solution iscycled from the tank, through the dosing module, and back to the tank.The return of the urea solution to the tank may sometimes interfere withoperation of the various sensors in the tank.

SUMMARY

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

An exhaust treatment fluid system includes a tank housing for storing anexhaust treatment fluid. A suction tube includes a first end positionedwithin the housing and a second end in communication with a suction portof the housing. An elongated laminar flow device is secured to adischarge port of the housing such that exhaust treatment fluid flowsalong surfaces thereof as the exhaust treatment fluid is returned to thetank housing. The laminar flow device includes a non-circularcross-section.

An exhaust treatment fluid system includes a tank housing for storing anexhaust treatment fluid. The tank is adapted to be fixed to a vehicle. Asuction tube is positioned within the tank. The exhaust treatment fluidsystem also includes an injector including an inlet in fluidcommunication with the suction tube and an outlet. An elongated laminarflow device is positioned with the tank housing and in fluidcommunication with the outlet. The exhaust treatment fluid flows throughthe outlet and is directed to flow across an external surface of thelaminar flow device.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 is a schematic representation of an exhaust system according to aprinciple of the present disclosure;

FIG. 2 is a cross-sectional view of a reagent tank according to aprinciple of the present disclosure;

FIG. 3 is a partial exploded-perspective view of the reagent tankillustrated in FIG. 2;

FIGS. 4-9 are cross-sectional views of a laminar flow device anddischarge tube according to a principle of the present disclosure;

FIG. 10 is a cross-sectional perspective view of a mounting plateincluding a suction tube, discharge tube, and a laminar flow deviceaccording to a principle of the present disclosure;

FIG. 11 is a cross-sectional view of a reagent tank according to aprinciple of the present disclosure;

FIG. 12 is a cross-sectional view of a reagent tank according to aprinciple of the present disclosure;

FIG. 13 is a fragmentary perspective view of a sensor assembly accordinganother principle of the present disclosure;

FIGS. 14 and 15 are perspective views of a skirt associated with thesensor assembly depicted in FIG. 13;

FIG. 16 is an exploded perspective view of an alternate skirtconstructed in according with the teachings of the present disclosure;

FIG. 17 is a flow chart illustrating a control scheme associated withthe sensors of an exhaust treatment fluid system;

FIG. 18 is a flow chart illustrating an alternate control scheme for theexhaust treatment fluid system; and

FIG. 19 is another flow chart depicting another alternate control schemeassociated with the sensors of an exhaust treatment fluid system.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

Example embodiments will now be described more fully with reference tothe accompanying drawings.

FIG. 1 schematically illustrates an exhaust system 10 according to thepresent disclosure. Exhaust system 10 can include at least an engine 12in communication with a fuel source (not shown) that, once consumed,will produce exhaust gases that are discharged into an exhaust passage14 having an exhaust after-treatment system 16. Downstream from engine12 can be disposed an exhaust treatment component 18, which can be aDOC, a DPF component or, as illustrated, a SCR component 20. Althoughnot required by the present disclosure, exhaust after-treatment system16 can further include components such as a thermal enhancement deviceor burner 17 to increase a temperature of the exhaust gases passingthrough exhaust passage 14. Increasing the temperature of the exhaustgas is favorable to achieve light-off of the catalyst in the exhausttreatment component 18 in cold-weather conditions and upon start-up ofengine 12, as well as initiate regeneration of the exhaust treatmentcomponent 18 when the exhaust treatment component 18 is a DPF.

To assist in reduction of the emissions produced by engine 12, exhaustafter-treatment system 16 can include a dosing module 22 forperiodically dosing an exhaust treatment fluid into the exhaust stream.As illustrated in FIG. 1, dosing module 22 can be located upstream ofexhaust treatment component 18, and is operable to inject an exhausttreatment fluid into the exhaust stream. In this regard, dosing module22 includes an injector having an inlet in fluid communication with areagent tank 24 and a pump 26 by way of inlet line 28 to dose an exhausttreatment fluid such as diesel fuel or urea into the exhaust passage 14upstream of exhaust treatment component 18. The injector of dosingmodule 22 may also include an outlet in communication with reagent tank24 via return line 30. Return line 30 allows for any exhaust treatmentfluid not dosed into the exhaust stream to be returned to reagent tank24. Flow of the exhaust treatment fluid through inlet line 28, dosingmodule 22, and return line 30 also assists in cooling the injector ofdosing module 22 so that dosing module 22 does not overheat. Dosingmodules 22 may be configured to include a cooling jacket that passes acoolant around dosing module 22 to cool it.

The amount of exhaust treatment fluid required to effectively treat theexhaust stream can also be dependent on the size of the engine 12. Inthis regard, large-scale diesel engines used in locomotives, marineapplications, and stationary applications can have exhaust flow ratesthat exceed the capacity of a single dosing module 22. Accordingly,although only a single dosing module 22 is illustrated for urea dosing,it should be understood that multiple dosing modules 22 for ureainjection are contemplated by the present disclosure.

The amount of exhaust treatment fluid required to effectively treat theexhaust stream may also vary with load, engine speed, exhaust gastemperature, exhaust gas flow, engine fuel injection timing, desiredNO_(x) reduction, barometric pressure, relative humidity, EGR rate andengine coolant temperature. A NO_(x) sensor or meter 32 may bepositioned downstream from SCR 20. NO_(x) sensor 32 is operable tooutput a signal indicative of the exhaust NO_(x) content to an enginecontrol unit 34. All or some of the engine operating parameters may besupplied from engine control unit (ECU) 34 via the engine/vehicledatabus to an exhaust after-treatment system controller 36. Thecontroller 36 could also be included as part of the engine control unit34. Exhaust gas temperature, exhaust gas flow and exhaust back pressureand other vehicle operating parameters may be measured by respectivesensors, as indicated in FIG. 1.

A temperature of the exhaust treatment fluid may also be a parametermonitored by exhaust after-treatment system controller 36. To monitor atemperature of the exhaust treatment fluid, reagent tank 24 may includea temperature sensor 40 located therein. As best shown in FIG. 2,reagent tank 24 can include a tank housing 42. Tank housing 42 may beformed of materials such as polyethylene, polypropylene, polystyrene,aluminum, steel, or any other type of material suitable for storing areagent exhaust treatment fluid 44 such as urea. To re-fill tank 24 withan exhaust treatment fluid, tank 24 may include an inlet 46 defined by athreaded neck 48 that may receive a removable cap 50 having a threadingthat corresponds to that of neck 48, as is known in the art.

Within tank housing 42 can be a pair of suction and discharge tubes 52and 54, respectively. Suction tube 52 communicates with pump 26downstream such that when pump 26 is activated, the urea exhausttreatment fluid 44 is drawn from tank 24 into inlet line 28. As notedabove, inlet line 28 communicates with dosing module 22 to provide ureaexhaust treatment fluid to the exhaust stream. If the urea exhausttreatment fluid 44 is not dosed into the exhaust stream, the ureaexhaust treatment fluid 44 may travel back to tank 24 through returnline 30. Return line 30 communicates with discharge tube 54. Each ofsuction tube 52 and discharge tube 54 may be secured within tank 24using a bulkhead or mounting plate 55 that may sit atop tank 24. Thebulkhead may sealingly engage a single opening (not shown) extendingthrough tank housing 42.

To monitor an amount of urea exhaust treatment fluid 44 in tank 24, afluid level indicating device 56 may be coupled to discharge tube 54. Inthe illustrated embodiment, fluid level indicating device 56 maycomprise an ultrasonic sensor device 58 that emits ultrasonic waves 60.Ultrasonic sensor device 58 may be positioned on a support member 59that is coupled to suction tube 52. Ultrasonic waves 60 may be emittedby ultrasonic sensor device 58 towards a surface 62 of the exhausttreatment fluid 44, which are then reflected by surface 62 back towardultrasonic sensor device 58. The time it takes ultrasonic waves 60 toreflect off surface 62 and return to ultrasonic sensor device 58 can bemeasured by controller 36 to determine an amount of fluid 44 remainingin tank 24. In this regard, ultrasonic sensor device 58 communicateswith controller 36.

An exhaust treatment fluid heater 64 may also be positioned in tank 24.Fluid heater 64 is designed to raise a temperature of the exhausttreatment fluid 44, particularly in cold-weather conditions where theexhaust treatment fluid 44 can freeze. Fluid heater 64 may be aresistive heater, or may be configured to allow flow of an enginecoolant therethrough, without limitation. Fluid heater 64 does notnecessarily continuously operate during operation of engine 12. Rather,fluid heater 64 communicates with controller 36 such that fluid heater64 can be activated as needed. In this regard, a temperature of theexhaust treatment fluid 44 can be transmitted to controller 36 fromtemperature sensor 40. If the sensed temperature is too low, controller36 can instruct fluid heater 64 to activate to heat or thaw the exhausttreatment fluid 44.

Temperature sensor 40 may be positioned anywhere within tank 24satisfactory to properly determine a temperature of the exhausttreatment fluid 44. For example, temperature sensor 40 can be attachedto an interior wall 66 of housing 42. Alternatively, temperature sensor40 may be attached to suction tube 52 or discharge tube 54.

Tank 24 may also include a concentration sensor 68. Concentration sensor68 may be fixed to interior wall 66, or may be secured to suction tube52, discharge tube 54, or another structure, without departing from thescope of the present disclosure. Concentration sensor 68 is operable todetermine a concentration of the urea exhaust treatment fluid 44, whichcan be particularly advantageous to determine whether a fluid (e.g.,water) other than urea exhaust treatment fluid 44 has been provided totank 24. If a concentration of the exhaust treatment fluid 44 isdetermined by controller 36 to be above or below a predetermined value,controller 36 may signal an error flag that prevents dosing by dosingmodule 22, or prevents engine 12 from operating until a correctconcentration of fluid 44 is achieved. Alternatively, controller 36 mayadjust the dosing to account for the present concentration.

To determine a concentration of the exhaust treatment fluid 44,concentration sensor 68 may be an ultrasonic sensor that is operable toemit ultrasonic waves 61 into the exhaust treatment fluid. Other typesof non-ultrasonic sensors are within the scope of the presentdisclosure. In the illustrated exemplary embodiment, concentrationsensor 68 may be disposed proximate ultrasonic sensor device 58 and mayemit ultrasonic waves 61, which may then be reflected off ultrasonicsensor device 58. Alternatively, a reflective member (not shown) may bedisposed between concentration sensor 68 and ultrasonic sensor device 58to reflect ultrasonic waves 61. Another alternative is to haveconcentration sensor 68 face and emit ultrasonic waves 61 towardinterior wall 66 for reflection therefrom. Regardless, based on thevelocity of the ultrasonic waves 61, controller 36 may determine aconcentration of the exhaust treatment fluid 44. Although fluid levelindicating device 56 and concentration sensor 68 are illustrated asbeing distinct components within tank 24, it should be understood that asingle sensor (e.g., ultrasonic sensor device 58) can be used forlevel-sensing and concentration-sensing without departing from the scopeof the present disclosure.

When engine 12 or exhaust after-treatment system 16 are not operating(i.e., no exhaust treatment fluid is being dosed into the exhauststream), any exhaust treatment fluid 44 present in dosing module 22,inlet line 28, return line 30, and pump 26 can freeze in coldtemperatures. To prevent freezing of the exhaust treatment fluid 44 inthe dosing module 22, inlet line 28, return line 30, and pump 26, pump26 is operable to run in reverse to purge each of these elements. Afterpurging, pump 26 may be primed to pressurize the inlet line 28 anddosing module 22 before the exhaust treatment fluid 44 is dosed into theexhaust stream. During priming, the unused exhaust treatment fluid 44returns from dosing module 22 to tank 24 via the return line 30.

In addition to the unused exhaust treatment fluid 44, air may also bepresent in the unused exhaust treatment fluid 44 that was previouslylocated within the tank 24. Due to the presence of air in the unusedexhaust treatment fluid 44, bubbles may develop as the air is returnedto tank 24. These bubbles may then float to surface 62 throughperforations 57 formed in discharge tube 54, and remain at surface 62for a period of time such surface 62 becomes frothy. The bubbles andfrothy surface 62 are not conducive to determining a proper fluid levelwithin tank 24 by ultrasonic sensor device 58, or a proper concentrationby concentration sensor 68. That is, the bubbles may provide aninaccurate surface level 62 that prevents controller 36 from properlymeasuring reflections of ultrasonic waves 60 and 61 by ultrasonic sensordevice 58. The bubbles may also interfere with concentration sensor 68in that the bubbles may remain suspended in the exhaust treatment fluid44 and cause a density change in the exhaust treatment fluid 44 that isbeing monitored by concentration sensor 68.

To assist in preventing formation of bubbles as the exhaust treatmentfluid 44 is cycled back to tank 24, a laminar flow device 70 may bedisposed in discharge tube 54. Laminar flow device 70, as bestillustrated in FIG. 3, may be an elongate member having a lengthsubstantially equal to that of discharge tube 54. Laminar flow device 70is generally non-circular in cross-section, and has a diameter that isless than that of discharge tube 54 so that laminar flow device 70 mayfit within discharge tube 54. The non-circular cross-section of laminarflow device allows for the presence of an air-gap 72 (FIG. 4) betweenlaminar flow device 70 and an interior surface 74 of discharge tube 54.

The exhaust treatment fluid 44 will tend to flow along surfaces 76 oflaminar flow device 70, while any air present in the return flow maytravel in air-gap 72 located between laminar flow device 70 and aninterior surface 74. As air travels in air-gap 72, it can be expelledinto tank 24 through perforations 57 before travelling beneath level 62of fluid 44. In this manner, bubbles are prevented, or at leastsubstantially minimized, from occurring that can interfere withultrasonic sensor device 58. It should be understood that although theabove-noted exemplary embodiment described use of laminar flow device 70in conjunction with discharge tube 54, the present disclosure should notbe limited thereto. In this regard, the present disclosure contemplatesconfigurations where laminar flow device 70 is used in lieu of dischargetube 54.

Although laminar flow device 70 is illustrated as including astar-shaped cross-section in FIG. 4, the present disclosure should notbe limited thereto. Laminar flow device 70 can include any non-circularcross-section known to one skilled in the art. For example, FIG. 5illustrates laminar flow device 70 having a triangular cross-section.FIG. 6 illustrates laminar flow device 70 having a Y-shapedcross-section. FIG. 7 illustrates a planar laminar flow device 70. FIG.8 illustrates a laminar flow device 70 having a cross-shapedcross-section. FIG. 9 illustrates a laminar flow device 70 having asquare-shaped cross-section.

As best shown in FIG. 10, laminar flow device 70 may include a threadedend 78. Threaded end 78 may correspond to a threading 80 formed in anaperture 82 of mounting plate 55. After laminar flow device 70 isthreadingly engaged with mounting plate 55, discharge tube 54 may beslip fit about laminar flow device. In the arrangement depicted in FIG.10, discharge tube 54 is press-fit within a counterbore 83 of mountingplate 55. In contrast to laminar flow device 70 being threadinglyengaged with mounting plate 55, suction tube 52 can be press-fit withinan aperture 84 of mounting plate. Alternatively, suction tube 52 andaperture 84 can each include threadings to secure suction tube 52 toaperture 84. In another configuration, laminar flow device 70 may bepress-fit within discharge tube 54.

FIG. 10 also includes arrows having a solid outline depicting the flowof urea when the pump is operating to provide pressurized fluid todosing module 22. Arrows having a dashed line representation indicatethe flow of air through the system as pump 26 is operating in the purgemode to drive the unused exhaust treatment fluid 44 toward tank 24. Apair of apertures 85 a, 85 b, positioned near mounting plate 55 toprovide a path for air flow from tank 24 to discharge tube 54.

Now referring to FIG. 11, another exemplary configuration of tank 24 isillustrated. Tank 24 includes a discharge tube 54 that is configured toallow air to escape from perforations 57 formed therein, while allowingreturned exhaust treatment fluid to flow along interior surfacesthereof. In this regard, discharge tube 54 may be configured to have azig-zag configuration. Although a zig-zag configuration is illustrated,it should be understood that discharge tube 54 can be helical or spiralwithout departing from the scope of the present application.

In another exemplary embodiment of the present disclosure depicted inFIG. 12, a protective skirt or fence 86 may be disposed about ultrasonicsensor device 58 and concentration sensor 68. As noted above,concentration sensor 68 may be designed to emit ultrasonic waves 61(FIG. 2) toward ultrasonic sensor device 58, which then reflectsultrasonic waves back toward concentration sensor 68. If bubblesproduced by cycling the exhaust treatment fluid 44 back into tank 24 arepresent at locations proximate concentration sensor 68 and ultrasonicsensor device 58, an improper concentration reading may occur due to achange in density of the exhaust treatment fluid and unnecessaryreflections of ultrasonic waves 61.

Protective skirt 86 may be fixed to a bottom surface 88 of tank 24, andperipherally surrounds ultrasonic sensor device 58 and concentrationsensor 68. A region 90 defined by an interior of skirt 86 is therebyprovided where ultrasonic sensor device 58 and concentration sensor 68may be positioned. Skirt 86 has a height H that extends past a locationwhere ultrasonic sensor device 58 and concentration sensor 68 arepositioned. Bubbles, therefore, are prevented from entering region 90and interfering with ultrasonic sensor device 58 and concentrationsensor 68. It should be understood that although skirt 86 is illustratedas being fixed to bottom surface 88 of tank 24, the present disclosureshould not be limited to such a configuration. In contrast, skirt 86 maybe fixed to other members such as suction tube 52, or may be fixed to asupport member 59, so long as bubbles are prevented from entering thespace 92 between ultrasonic sensor device 58 and concentration sensor68.

Although not explicitly shown in FIG. 12, it should be understood thatdischarge tube 54 may include laminar flow device 70 therein. That is,tank 24 can be configured to include each of skirt 86 and laminar flowdevice 70. It should also be appreciated that skirt 86 may include aplurality of perforations that allow exhaust treatment fluid 44 to enterregion 90, while preventing bubbles from entering.

FIG. 13-15 depict a portion of a sensor assembly 100 that may bepositioned within tank 24 as a structure separate from suction tube 52and discharge tube 54. Sensor assembly 100 may be fixed to any number ofcomponents including mounting plate 55, tank 24, suction tube 52 and/ordischarge tube 54. Sensor assembly 100 includes a body 102 including afirst tube 104 extending substantially vertically and parallel to asecond tube 106. Body 102 may be molded from a plastic material suchthat first tube 104 is integrally formed with second tube 106. A beam110 may be constructed as a separate component and coupled to first tube104 and second tube 106 or may be integrally formed with body 102.

When installed within tank 24, first tube 104 is in receipt of exhausttreatment fluid 44 via an aperture 108 extending through first tube 104.Second tube 106 is in receipt of wires 109 coupled to concentrationsensor 68 and any other electrical element that may be coupled to beam110. For example, it is contemplated that a temperature sensor 112 isfixed to beam 110. Another optional configuration may include a heatingelement 114 coupled to beam 110. Depending on the temperature of exhausttreatment fluid 44 sensed by temperature sensor 112, heating element 114may be selectively energized. Wires 109 and possibly one or morecontrollers may be positioned within second tube 106.

A skirt 118 is removably coupled to body 102. Skirt 118 functionssubstantially similarly to skirt 86 previously described. Skirt 118 ispreferably a one-piece molded plastic cover that may be coupled to body102 in a snap-fit manner. Other forms of attachment including screws ora press fit are also within the scope of the present disclosure. Skirt118 includes a continuous wall 120, a top 122, a first leg 124 and asecond leg 126. A substantially figure-eight shaped aperture 128 extendsthrough top 122 to allow first tube 104 and second tube 106 to passtherethrough. A notch 130 is located along an edge of aperture 128,sized and positioned to engage a protrusion extending from first tube104 to restrict rotation of skirt 118 relative to body 102. Apertures132, 134, extend through top 122 to allow air that may be positionedunder skirt 118 to escape. A rib 138 connects side wall 120 with top 122to provide skirt 118 with a predetermined stiffness. The predeterminedstiffness is less than would be provided with a completely rigidstructure. Accordingly, opposing portions of side wall 120 identified atreference numerals 140 a, 140 b, may flex relative to one another toaccommodate for an increase in volume that occurs when exhaust treatmentfluid 44 freezes within tank 24. A flexible skirt 118 is provided thatwill not fracture when forces are applied due to the freezing of theexhaust treatment fluid 44.

Skirt 118 is constructed from a flexible material that allows legs 124,126 to be temporarily elastically deformed such that a first catch 144and a second catch 146 are displaced from a free state position to passby beam 110. Once the extent of beam 110 has been passed, legs 124, 126elastically return to their free state orientation to position catch 144and catch 146 adjacent to a retention surface 148 of beam 110.

Apertures 150, 152, extend through wall 120 and allow exhaust treatmentfluid 44 to pass through skirt 118 and contact concentration sensor 68.Some of the fluid that passes through apertures 150, 152 may also enterfirst tube 104 via aperture 108. Another exhaust treatment fluid passageis provided in a space 153 between an edge 154 of side wall 120 and asurface 158 of beam 110. With this arrangement, a portion of edge 154engages a surface 160 of beam 110 while another portion of edge 154 isspaced apart from beam 110 to allow a restricted flow of fluid 44 fromthe main body of tank 24 under skirt 118. Apertures 150, 152 and gap 153are sized to allow fluid flow but restrict entry of bubbles under skirt118. Apertures 132, 134 are also particularly sized to be relativelysmall to allow air that may be trapped under skirt 118 to exit whilealso minimizing ingress of bubbles. It should be appreciated that thesnap fit coupling including inwardly extending catches 144, 146 ismerely exemplary and other mechanisms for securing skirt 118 to any oneof first tube 104, second tube 106 or beam 110 are within the scope ofthe present disclosure.

FIG. 16 depicts an alternate skirt 118 a. Skirt 118 a is substantiallysimilar to skirt 118 with the exception that a first half 168 isseparable from a second half 170. A plurality of prongs 172 extend fromfirst half 168. Prongs 172 are configured for snap-fit coupling to aplurality of receptacles 174 in second half 170. When prongs 172 arereceived within receptacles 174, first half 168 is fixed to second half170. The remaining features of skirt 118 a are substantially the same asskirt 118. The similar features are identified with like numeralsincluding an “a” suffix. By configuring skirt 118 a as a two pieceassembly, manufacturing processes may be simplified with regard toforming first tube 104, second tube 106 and beam 110 as well as theinterconnection of these components with skirt 118 a.

The above-described exemplary embodiments assist in preventing bubblesgenerated during a purge/prime cycle from interfering with the levelsensor device 58 and concentration sensor 68 as these sensors measurethe level and concentration of the exhaust treatment fluid 44. If tank24 is not provided with laminar flow device 70 or skirt 86, however, thegeneration of bubbles can interfere with these sensors 58 and 68. Tofurther minimize interference with sensors 58 and 68, controller 36 maydelay operation of sensors 58 and 68 for a predetermined period of timeafter the priming cycle has completed. For example, controller 36 maydelay operation of sensors 58 and 68 for a period of time in the rangeof ten to twenty minutes. In such a case, any bubbles generated duringthe priming process may dissipate to an extent that will notsubstantially interfere with either ultrasonic sensor device 58 orconcentration sensor 68.

Another alternative to delaying operation of sensors 58 and 68 from theend of the priming cycle is to delay sensors 58 and 68 a predeterminedperiod of time from the start of the priming cycle. For example, and asdepicted in FIG. 17, the priming process can be controlled by controller36 to begin at a “Key On” condition 200. Pump priming starts at block210. A timer counts for a first predetermined period of time at block220 (e.g., five minutes). Knowing that the priming process takes acertain amount of time to complete, the output from sensors 58 and 68may be ignored during the first predetermined period of time until thetimer turns off at block 230 (e.g., fifteen to twenty-five minutes).Once the set time has elapsed, control proceeds to block 240. Controlassesses the outputs from the sensors 58, 68 and determines whether newfault codes based on the signals received from sensors 58, 68 should bebroadcast per standard operation procedure.

FIG. 18 provides a flow chart for an alternate control schemesubstantially similar to the control previously described in relation toFIG. 17. Accordingly, similar elements will be identified with likereference numerals increased by 100. For example “Key On” block 300 issubstantially similar to block 200. At block 315, a current value forone of the sensors previously described, such as concentration sensor 68or ultrasonic sensor device 58, is compared with the last stored valuefrom the same sensor. At block 320, control determines whether thedifference between the recently acquired sensor value and the laststored value is beyond a predetermined range. If so, control starts thetimer and ignores the sensor outputs as previously described. Once thetimer is turned off, a recently acquired sensor value is compared withthe previously stored value at block 335. At block 340, controldetermines whether a new fault code warning should be broadcast based onthe comparison performed in block 335. The control scheme outlined inFIG. 18 may be applied to any one or more sensors within the exhausttreatment fluid storage tank as desired.

FIG. 19 provides a flow chart for another alternate control scheme thatis substantially similar to the control described in relation to FIG.18. Accordingly, similar elements will be identified with like referencenumerals increased by 100. Block 415 differs from block 315 in thatcurrent values from both concentration sensor 68 and ultrasonic sensordevice 58 are compared with historical values from each of thesesensors. At block 420, control determines if both of the currentlydetermined values are out of their respective ranges relative to thehistorical data. If so, a time period in which the fault codes areignored begins. By implementing a control strategy that requires both ofthe sensors to have current readings that are out of range, thelikelihood of broadcasting a false fault code warning is minimized. Forexample, if only the exhaust treatment fluid level sensor data isutilized in the control, a fault code warning may be issued based on thevehicle operator filling tank 24 with exhaust treatment fluid prior to“Key On” at block 400. Referring again to FIG. 19, once the timer isturned off at block 430, control compares the current sensor values forboth the quality sensor and the level sensor with historical values atblock 435. New fault code warnings are broadcast at block 440, ifmerited.

The foregoing description of the embodiments has been provided forpurposes of illustration and description. It is not intended to beexhaustive or to limit the disclosure. Individual elements or featuresof a particular embodiment are generally not limited to that particularembodiment, but, where applicable, are interchangeable and can be usedin a selected embodiment, even if not specifically shown or described.For example, an alternate fluid level indicating device 56 a may becoupled to sensor assembly 100. As shown in FIG. 13, fluid levelindicating device 56 a includes a float 180 positioned within first tube104. Float 180 rests on the surface of the exhaust treatment fluidwithin first tube 104. As previously mentioned, fluid may enter firsttube 104 via apertures 150 on skirt 118 and aperture 108 extendingthrough the wall of first tube 104. Float 180 may be coupled to a switch(not shown) or a sensor indicating the position of float 180 withinfirst tube 104. The switch or associated sensor is operable to output asignal indicative of the level of exhaust treatment fluid within tank24. The same may also be varied in many ways. Such variations are not tobe regarded as a departure from the disclosure, and all suchmodifications are intended to be included within the scope of thedisclosure.

What is claimed is:
 1. An exhaust treatment fluid system, comprising: atank housing for storing an exhaust treatment fluid including a suctionport and a discharge port; a suction tube having a first end positionedwithin the housing and a second end in communication with the suctionport; and an elongated laminar flow device secured to the discharge portsuch that exhaust treatment fluid flows along surfaces thereof as theexhaust treatment fluid is returned to the tank housing, wherein thelaminar flow device includes a non-circular cross-section.
 2. Theexhaust treatment fluid system of claim 1, further comprising adischarge tube positioned within the tank housing and secured at thedischarge port, wherein the laminar flow device is positioned within thedischarge tube.
 3. The exhaust treatment fluid system of claim 1,wherein the discharge tube includes an inner surface, and thenon-circular cross-section of the laminar flow device provides anair-gap between surfaces of the laminar flow device and the innersurface of the discharge tube.
 4. The exhaust treatment fluid system ofclaim 1, wherein the laminar flow device cross-section is square.
 5. Theexhaust treatment fluid system of claim 1, wherein the laminar flowdevice cross-section is triangular.
 6. The exhaust treatment fluidsystem of claim 1, wherein the laminar flow device cross-section isY-shaped.
 7. The exhaust treatment fluid system of claim 1, wherein thelaminar flow device cross-section is cross-shaped.
 8. The exhausttreatment fluid system of claim 1, wherein the laminar flow devicecross-section is star-shaped.
 9. The exhaust treatment fluid system ofclaim 1, wherein the laminar flow device cross-section includes a planarsurface.
 10. The exhaust treatment fluid system of claim 1, furthercomprising a sensor for determining at least one of a fluid level of theexhaust treatment fluid and a concentration of the exhaust treatmentfluid, the sensor being positioned within the tank housing.
 11. Theexhaust treatment fluid system of claim 10, further including acontroller determining whether to broadcast a fault code warning basedon a signal output from the sensor, the controller ignoring the signalfor a predetermined amount of time before determining whether tobroadcast the fault code warning.
 12. The exhaust treatment fluid systemof claim 11, wherein the predetermined amount of time begins when a pumppumping the exhaust treatment fluid begins to prime.
 13. The exhausttreatment fluid system of claim 11, wherein the controller compares thesignal output from the sensor with a previously stored value anddetermines whether to start ignoring the signal based on the comparisonof the signal to the previously stored value.
 14. The exhaust treatmentfluid system of claim 10, further including another sensor positionedwithin the tank and determining the other of the fluid level and theconcentration of the exhaust treatment fluid.
 15. The exhaust treatmentfluid system of claim 14, wherein the controller compares a signaloutput from the sensor and a signal output from the another sensor withpreviously stored values and determines whether to start a timer duringwhich the signals are ignored based on the comparison of the signals tothe previously stored values.
 16. The exhaust treatment fluid system ofclaim 15, wherein the signals from the sensor and the another sensor areignored only if both signals are out of a desired range when compared tothe previously stored values.
 17. The exhaust treatment fluid system ofclaim 14, further including a temperature sensor positioned in proximityto the sensor and the another sensor.
 18. The exhaust treatment fluidsystem of claim 1, further comprising a bulkhead sealingly engaging thetank housing, the suction tube and the laminar flow device being fixedto the bulkhead.
 19. The exhaust treatment fluid system of claim 1,wherein the laminar flow device includes a threaded end coupled to thetank and a free opposite end.
 20. The exhaust treatment fluid system ofclaim 1, wherein the laminar flow device is positioned in a non-verticalorientation.
 21. An exhaust treatment fluid system, comprising: a tankhousing for storing an exhaust treatment fluid, the tank being adaptedto be fixed to a vehicle; a suction tube positioned within the tank; aninjector including an inlet in fluid communication with the suction tubeand an outlet; and an elongated laminar flow device positioned withinthe tank housing and in fluid communication with the outlet, the exhausttreatment fluid flowing through the outlet and being directed to flowacross an external surface of the laminar flow device.
 22. The exhausttreatment fluid system of claim 21, further including a discharge tubepositioned within the tank, in fluid communication with the outlet, andsurrounding the laminar flow device, wherein the exhaust treatment fluidthat flows through the outlet also flows through the discharge tube. 23.The exhaust treatment fluid system of claim 22, wherein the suction tubeand the discharge tube each include open ends spaced apart from aninterior surface of the tank.
 24. The exhaust treatment fluid system ofclaim 22, wherein the laminar flow device extends an entire length ofthe discharge tube.
 25. The exhaust treatment fluid system of claim 22,further including a pump coupled to the suction tube and providingpressurized exhaust treatment fluid from the tank to the injector whendriven in a first direction, the pump being drivable in an oppositedirection to purge the exhaust treatment fluid from the injector. 26.The exhaust treatment fluid system of claim 21, wherein the laminar flowdevice includes a solid core precluding a flow of exhaust treatmentfluid therethrough.
 27. The exhaust treatment fluid system of claim 21,wherein the laminar flow device cross-section is cross-shaped.